Memory system with command mixing for timing control

ABSTRACT

A memory system includes a memory controller and a memory. The memory controller selectively operates in a first mode and a second mode. In the first mode, the memory controller transmits a first command continuously during a plurality of clock cycles. In the second mode, the memory controller to mix a second command with the first command and transmit the mixture of the first command and the second command. The memory changes command latch timing depending on the first or second mode.

CROSS-REFERENCE TO RELATED APPLICATION

Korean Patent Application No. 10-2015-0126786, filed on Sep. 8, 2015,and entitled, “Memory System,” is incorporated by reference herein inits entirety.

BACKGROUND

1. Field

One or more embodiments described herein relate to a memory system.

2. Description of the Related Art

Efforts are continually being made to reduce the size and number ofinput/output pads of memory devices. At the same time, attempts arebeing made to increase capacity and operation speed in order to enhanceperformance.

Reducing the number of input/output pads of a memory device may involvedecreasing the number of pads for receiving commands. The commands mayinclude, for example, addresses. As memory capacity increases, thenumber of pads (e.g., address pads) may decrease, while the number ofbits of the address may increase. Thus, commands may be transferred overa plurality of clock cycles.

When a command is transferred over a plurality of clock cycles, the timeduration for transferring the command through a corresponding commandpad may exceed the time duration for transferring data through datapads. This may cause inefficiencies or otherwise may disruptperformance.

SUMMARY

In accordance with one or more embodiments, a memory system includes amemory controller to selectively operate in a first mode and a secondmode, the memory controller to transmit a first command continuouslyduring a plurality of clock cycles in the first mode and the memorycontroller to mix a second command with the first command and transmitthe mixture of the first command and the second command in the secondmode; and a memory to change command latch timing depending on the firstmode or the second mode.

The memory controller may insert the second command between the clockcycles of the first command in the second mode. The memory may receiveflag information representing whether the second command is insertedbetween the clock cycles of the first command. When the flag informationrepresents that the second command is inserted between the clock cyclesof the first command, the memory may latch a second portion of the firstcommand after a standby time from a time point of latching a firstportion of the first command. The standby time may be determined basedon mode register information provided from the memory controller and isto be stored in a mode register of the memory device. The memorycontroller may generate the first command including the flaginformation.

The memory controller may combine the first command and the secondcommand as a third command to transmit the third command in the secondmode. The third command may include a row address and a column address.The first command may be an active command including a row address, andthe second command may be a column address strobe (CAS) commandincluding a column address.

The memory controller may transmit the active command during 4 clockcycles and transmit the CAS command during 2 clock cycles aftertransmitting the active command in the first mode; and transmit a firstportion of the active command during 2 clock cycles, transmit the CAScommand during 2 clock cycles after transmitting the first portion ofthe active command, and transmit a second portion of the active commandafter transmitting the CAS command in the second mode. The memorycontroller may transmit the active command during 4 clock cycles andtransmit the CAS command during 2 clock cycles after transmitting theactive command in the first mode; and combine the first command and thesecond command as a third command and transmit the third command during4 clock cycles in the second mode. A data transfer time for a singleaccess operation may be substantially equal to a CAS-to-CAS delay time(tCCD) between two sequential CAS commands for two sequential accessoperations.

When a first access operation and a second access operation areperformed successively, the memory controller may transmit a firstactive command for the first access operation; may transmit a firstportion of a second active command for the second access operation aftertransmitting the first active command; may transmit a first CAS commandfor the first access operation after transmitting the first portion ofthe second active command; may transmit a second portion of the secondactive command after transmitting the first CAS command; and maytransmit a second CAS command for the second access operation aftertransmitting the second portion of the second active command. The memorydevice may be a three-dimensional semiconductor memory device includinga plurality of semiconductor dies that are stacked vertically.

In accordance with one or more other embodiments, a memory systemincludes a memory controller to selectively operate in a first mode anda second mode, the memory controller to transmit an active commandincluding a row address continuously during a plurality of clock cyclesin the first mode and the memory controller to mix a column addressstrobe (CAS) command including a column address with the active commandand transmit a mixture of the active command and the CAS command in thesecond mode; and a memory device to change command latch timingdepending on the first mode or the second mode.

In accordance with one or more other embodiments, an apparatus includesan interface coupled to a memory; and a memory controller to selectivelyoperate in a first mode and a second mode, the memory controller totransmit a first command continuously through the interface during aplurality of clock cycles in the first mode and to mix a second commandwith the first command and transmit the mixture of the first command andthe second command through the interface in the second mode. The memorycontroller may insert the second command between the clock cycles of thefirst command in the second mode. The memory controller may include flaginformation in the first command transmitted through the interface tothe memory, wherein the flag information is indicative of a change incommand latch timing for the memory.

BRIEF DESCRIPTION OF THE DRAWINGS

Features will become apparent to those of skill in the art by describingin detail exemplary embodiments with reference to the attached drawingsin which:

FIG. 1 illustrates an embodiment of a method for operating a memorysystem;

FIG. 2 illustrates an embodiment of a memory system;

FIG. 3 illustrates an embodiment of a memory device;

FIG. 4 illustrates an example of commands for a memory system;

FIG. 5 illustrates an example of date transfer and command transfertimes;

FIG. 6 illustrates example operations in different modes of the memorysystem;

FIGS. 7 and 8 illustrate an example of signal transfer and command latchtiming in a first mode;

FIGS. 9 and 10 illustrate examples of signal transfer and command latchtiming in a second mode;

FIG. 11 illustrates an example of commands for a memory system;

FIG. 12 illustrates example operations in different modes of a memorysystem;

FIG. 13 illustrates an example of signal transfer in a second mode;

FIG. 14 illustrates an embodiment of a memory module;

FIG. 15 illustrates an embodiment of a stacked memory device;

FIG. 16 illustrates an embodiment of a memory system;

FIG. 17 illustrates an embodiment of a mobile system; and

FIG. 18 illustrates an embodiment of a computing system.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey exemplary implementations to those skilled in the art. Theembodiments may be combined to form additional embodiments.

In the drawings, the dimensions of layers and regions may be exaggeratedfor clarity of illustration. It will also be understood that when alayer or element is referred to as being “on” another layer orsubstrate, it may be directly on the other layer or substrate, orintervening layers may also be present. Further, it will be understoodthat when a layer is referred to as being “under” another layer, it maybe directly under, and one or more intervening layers may also bepresent. In addition, it will also be understood that when a layer isreferred to as being “between” two layers, it may be the only layerbetween the two layers, or one or more intervening layers may also bepresent. Like reference numerals refer to like elements throughout.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are used to distinguish oneelement from another. Thus, a first element discussed below could betermed a second element without departing from the teachings of thepresent disclosure. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it may be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.).

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting of thepresent disclosure. As used herein, the singular forms “a,” “an” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will be further understood thatthe terms “comprises” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

FIG. 1 illustrates an embodiment of a method for operating a memorysystem. Referring to FIG. 1, in a first mode, a first command iscontinuously transferred from a memory controller and a memory deviceduring a plurality of clock cycles (S100). In a second mode, a secondcommand is mixed with the first command and the mixture of the firstcommand and the second command is transferred from the memory controllerto the memory device (S200).

The first command may be, for example, an active command including a rowaddress. The second command may include, for example, a column addressstrobe (CAS) command including a column address. The CAS command may bea read command indicating a read operation or a write command indicatinga write operation. In one embodiment, the memory device may perform rowaddressing based on the row address provided with or in the activecommand, and then may perform column addressing based on the columnaddress provided with or in the CAS command. The first mode maycorrespond to an operation mode in which a plurality of commands for asingle operation are transferred sequentially, in a predetermined order,from the memory controller to the memory device.

The second mode may correspond to an operation mode in which the firstcommand and the second command are mixed. The mixed results are thentransferred from the memory controller to the memory device. In someexample embodiments, as described, for example, with reference to FIGS.6 to 10, the memory controller may insert the second command between theclock cycles of the first command in the second mode. In other exampleembodiments, as described, for example, with reference to FIGS. 11 to13, the memory controller may combine the first command and the secondcommand as a third command and transmit the third command in the secondmode.

In the memory device, command latch timing may be changed depending onthe first mode or the second mode (S300). For example, the memory devicemay receive flag information representing whether the second command isinserted between the clock cycles of the first command. In some exampleembodiments, as described, for example, with reference to FIG. 4, thememory controller may incorporate the flag information into the firstcommand and may provide the first command including the flag informationto the memory device. The memory device may change the command latchtiming depending on the first mode or the second mode based on the flaginformation in the first command. The change of the command latch timingmay be performed, for example, as indicated in FIGS. 7 to 9.

The memory system and the method of operating the memory systemaccording to example embodiments may reduce the tCCD by adopting thesecond mode for mixing the two commands. Through the reduction of thetCCD, the DQ bubble, in which data transfer is not performedcontinuously, may be prevented and utilization of the data bus may beenhanced.

FIG. 2 illustrates an embodiment of a memory system 10, and FIG. 3illustrates an embodiment of a memory device 400 in the memory system 10of FIG. 2. Referring to FIG. 2, the memory system 10 includes a memorycontroller 200 and a memory device 400. The memory controller 200 andthe memory device 400 includes respective interfaces for mutualcommunication. The interfaces may be connected through a control bus 21for transferring a command CMD, an address ADDR, a clock signal CLK,etc. and a data bus 22 for transferring data.

According to some standards for memory devices, the address ADDR may beincorporated in the command CMD as illustrated in FIG. 4. The memorycontroller 200 may generate the command CMD to control the memory device400 and the data may be written in or read from the memory device 400under the control of the memory controller 200. According to exampleembodiments, the memory controller 200 may selectively operate in afirst mode to transmit a first command continuously during a pluralityof clock cycles or a second mode to mix a second command with the firstcommand, and transmit a mixture of the first command and the secondcommand. The memory device 400 may change command latch timing dependingon the first mode or the second mode.

Referring to FIG. 3, the memory device 400 may include a control logic410, an address register 420, a bank control logic 430, a row addressmultiplexer 440, a refresh counter 445, a column address latch 450, arow decoder 460, a column decoder 470, a memory cell array 480, a senseamplifier unit 485, an input/output (I/O) gating circuit 490 and a datainput/output (I/O) buffer 495.

The memory cell array 480 may include a plurality of bank arrays 480a˜480 h. The row decoder 460 may include a plurality of bank rowdecoders 460 a˜460 h respectively coupled to the bank arrays 480 a˜480h. The column decoder 470 may include a plurality of bank columndecoders 470 a˜470 h respectively coupled to the bank arrays 480 a˜480h. The sense amplifier unit 485 may include a plurality of bank senseamplifiers 485 a˜485 h respectively coupled to the bank arrays 480 a˜480h.

The address register 420 may receive an address ADDR including a bankaddress BANK_ADDR, a row address ROW_ADDR, and a column address COL_ADDRfrom the memory controller. The address register 420 may provide thereceived bank address BANK_ADDR to the bank control logic 430, thereceived row address ROW_ADDR to the row address multiplexer 440, andthe received column address COL_ADDR to the column address latch 450.

The bank control logic 430 may generate bank control signals based onthe bank address BANK_ADDR. One of the bank row decoders 460 a˜460 hcorresponding to the bank address BANK_ADDR may be activated based onthe bank control signals. One of the bank column decoders 470 a˜470 hcorresponding to the bank address BANK_ADDR may be activated based onthe bank control signals.

The row address multiplexer 440 may receive the row address ROW_ADDRfrom the address register 420 and may receive a refresh row addressREF_ADDR from the refresh counter 445. The row address multiplexer 440may selectively output the row address ROW_ADDR or the refresh rowaddress REF_ADDR as a row address RA. The row address RA output from therow address multiplexer 440 may be applied to the bank row decoders 460a˜460 h.

The activated one of the bank row decoders 460 a˜460 h may decode therow address RA output from the row address multiplexer 440 and mayactivate a word-line corresponding to the row address RA. For example,the activated bank row decoder may apply a word-line driving voltage tothe word-line corresponding to the row address RA.

The column decoder 470 may include a column address latch (CAL) 450. Thecolumn address latch may receive the column address COL_ADDR from theaddress register 420 and temporarily store the received column addressCOL_ADDR. In some embodiments, in a burst mode, the column address latch450 may generate column addresses that increment from the receivedcolumn address COL_ADDR. The column address latch 450 may apply thetemporarily stored or generated column address to the bank columndecoders 470 a˜470 h.

The activated one of the bank column decoders 470 a˜470 h may decode thecolumn address COL_ADDR output from the column address latch 450 and maycontrol the input/output gating circuit 490 in order to output datacorresponding to the column address COL_ADDR.

The I/O gating circuit 490 may include circuitry for gating input/outputdata. The I/O gating circuit 490 may further include read data latchesfor storing data output from the bank arrays 480 a˜480 h and writedrivers for writing data to the bank arrays 480 a˜480 h.

Data to be read from one bank array of the bank arrays 480 a˜480 h maybe sensed by a sense amplifier 485 coupled to the one bank array fromwhich the data is to be read and may be stored in the read data latches.The data stored in the read data latches may be provided to the memorycontroller via the data I/O buffer 495. Data DQ to be written in onebank array of the bank arrays 480 a˜480 h may be provided to the dataI/O buffer 495 from the memory controller. The write driver may writethe data DQ in one bank array of the bank arrays 480 a˜480 h.

The control logic 410 may control operations of the memory device 400.For example, the control logic 410 may generate control signals for thememory device 400 in order to perform a write operation or a readoperation. The control logic 410 may include a command decoder 411 thatdecodes a command CMD received from the memory controller 200 and a moderegister set 412 that sets an operation mode of the memory device.

In some example embodiments, the control logic 410 may generate latchcontrol signals LTR and LTC, for example, as illustrated in FIGS. 7 and9, to control operation of the address register 420. The control logicmay generate the latch control signals LTR and LTC based on the flaginformation representing whether the second command is inserted betweenthe clock cycles of the first command.

FIG. 3 illustrates that the control logic 410 and the address register420 are distinct from each other. In another embodiment, the controllogic 410 and the address register 420 may be implemented as a singleinseparable circuit. In addition, FIG. 3 illustrates that the commandCMD and the address ADDR are provided as distinct signals. In anotherembodiment, the command CMD and the address ADDR may be provided ascombined signals, for example, as illustrated in FIG. 4.

FIG. 4 illustrates example commands which may be used in one embodimentof a memory system. In this embodiment, combinations of the chipselection signal CS and the command-address signals CA0˜CA6 representingan active command ACT, a read command RD, a write command WR and a moderegister write command MRW. Also, H indicates the logic high level, Lindicates the logic low level, R0˜R17 indicate bits of a row address RA,BA0˜BA3 indicate bits of a bank address BA, V indicates any one of thelogic low level and the logic high level, BL indicates a burst length,C4˜C9 indicate bits of a column address CA, MA0˜MA5 indicate a locationof the mode register in which the mode register write operation isperformed, OP0˜OP7 indicate the mode information to be written in themode register, and RE1˜RE4 indicate first through fourth rising edges ofa clock signal CK.

The active command ACT may include a first portion ACTa and a secondportion ACTb and the active command ACT may be transferred during aplurality of clock cycles, for example, during the four clock cycles asillustrated in FIG. 4. The active command ACT may include the bankaddress bits BA0˜BA3 and the row address bits R0˜R17. Also the activecommand ACT may include the flag information SPL representing whetherthe other command is inserted between the clock cycles of the activecommand ACT. The first logic level (e.g., logic low level L) of the flaginformation SPL may indicate the first mode or the normal mode in whichthe first portion ACTa and the second portion ACTb of the active commandACT are transferred continuously during a plurality of clock cycles. Thesecond logic level (e.g., logic high level H) of the flag informationSPL may indicate the second mode or the split mode in which the othercommand is inserted between the first portion ACTa and the secondportion ACTb of the active command ACT and the mixture of the activecommand ACT and the other command is transferred.

Each of the read command RD and the write command WR may include thebank address bits BA0˜BA3 and the column address bits C4˜C9 and may betransferred during a plurality of clock cycles, for example, during thetwo clock cycles as in FIG. 4.

The mode register write command MRW may include a first portion MRWa anda second portion MRWb. The mode register write command MRW may betransferred during a plurality of clock cycles, for example, during thefour clock cycles as illustrated in FIG. 4. The mode register writecommand MRW may include the mode register location bits MA0˜MA5 and themode information bits OP0˜OP7. Also, the mode register write command MRWmay include the flag information SPL representing whether the othercommand is inserted between the clock cycles of the mode register writecommand MRW.

The first logic level (e.g., logic low level L) of the flag informationSPL may indicate the first mode or the normal mode in which the firstportion MRWa and the second portion MRWb of the mode register writecommand MRW are transferred continuously during a plurality of clockcycles. The second logic level (e.g., logic high level H) of the flaginformation SPL may indicate the second mode or the split mode in whichthe other command is inserted between the first portion MRWa and thesecond portion MRWb of the mode register write command MRW and themixture of the mode register write command MRW and the other command istransferred.

FIG. 4 illustrates non-limiting examples of combinations of the chipselection signal CS and the command-address signals CA0˜CA6. In at leastone embodiment, combinations of signals representing the commands may bechanged in various ways.

FIG. 5 illustrating a timing diagram describing an example of a datatransfer time and a command transfer time. Referring to FIG. 5, thecommands ACT and RD may be transferred in synchronization with a mainclock signal MCK of a memory system. For example, the transfer time ofthe active command ACT may correspond to the four clock cycles of themain clock signal MCK and the transfer time of the read command RD maycorrespond to the four clock cycles of the main clock signal MCK. Assuch, the transfer time of the commands ACT and RD for the readoperation may correspond to the eight clock cycles of the main clocksignal MCK.

The data transfer time may be changed depending on the clock frequencyfor the data transfer, the burst length BL, etc. For example, the databits 0˜31 may be transferred in synchronization with the main clocksignal MCK or the data clock signal WCK having a doubled frequencyaccording to the configuration of the memory system.

When the burst length BL is 16 and the data transfer is synchronizedwith the main clock signal MCK, the 16 data bits 0˜16 may be transferredduring the 8 clock cycles of the main clock signal MCK. Thus, the datatransfer time may be equal to the command transfer time. When the burstlength BL is 32 and the data transfer is synchronized with the dataclock signal WCK, the 32 data bits 0˜31 may be transferred during the 8clock cycles of the main clock signal MCK. Thus, the data transfer timemay be equal to the command transfer time. When the burst length BL is16 and the data transfer is synchronized with the data clock signal WCK,the 16 data bits 0˜16 may be transferred during the 4 clock cycles ofthe main clock signal MCK. Thus, the data transfer time may be shorterthan the command transfer time.

The problem of utilization of the data bus may not be caused when thedata transfer time is equal to the command transfer time. However, theproblem of DQ bubble may be caused such that the data transfer may notbe performed continuously when the data transfer time is shorter thanthe command transfer time.

FIG. 6 illustrates a timing diagram of example operations in a firstmode and a second mode. Referring to FIG. 6, the command may bedetermined as the combination of the chip selection signal CS and thecommand-address signals CA at the rising edges T1˜T9 of the main clocksignal MCK. The examples of the combination of the chip selection signalCS and the command-address signals CA are illustrated in FIG. 4. FIG. 6illustrates the command-address signals CAn in the first mode and thecommand-address signals CAm in the second mode.

The first command may be transferred continuously during a plurality ofclock cycles in the first mode. The mixture of the first command and thesecond command may be transferred in the second mode. As illustrated inFIG. 6, the first command may be the active command ACT and the secondcommand may be the CAS command. FIG. 6 illustrates the read command RDas an example of the CAS command and the CAS command may be the writecommand WR.

The memory controller 200 in FIG. 2 may transmit the active command ACTduring the four clock cycles corresponding to the four rising edges T3,T4, T5, and T6 of the main clock signal MCK. The memory controller 200may then transmit the CAS command RD during the two clock cyclescorresponding to the two rising edges T7 and T8 in the first mode. Theflag information SPL in the active command ACT may be at logic low levelL.

In contrast, the memory controller 200 may transmit the first portionACTa of the active command ACT during the two clock cycles correspondingto the two rising edges T1 and T2. The memory controller 200 maytransmit the CAS command RD during the two clock cycles corresponding tothe two rising edges T3 and T4. The memory controller 200 may thentransmit the second portion ACTb of the active command ACT during thetwo clock cycles corresponding to the two rising edges T5 and T6 in thesecond mode. The flag information SPL in the first portion ACTa of theactive command ACT may be at logic high level H.

As illustrated in FIG. 6, the CAS-to-CAS delay time (tCCD) correspondingto the time duration between the two successive CAS commands may bereduced by adopting the second mode for mixing the two commands. ThetCCDn in the first mode corresponds to the 6 clock cycles but the tCCDmin the second mode may be reduced to the 4 clock cycles. Through thereduction of the tCCD, the DQ bubble, in which data transfer is notperformed continuously, may be prevented and utilization of the data busmay be enhanced.

FIGS. 7 and 8 are timing diagrams illustrating an example of a signaltransfer and a command latch timing in a first mode. In particular, FIG.7 illustrates command transfer and command latch timing in the firstmode or the normal mode when a first access operation and a secondaccess operation are performed successively. FIG. 8 illustratescorresponding data transfer. As described above, the command may bedetermined as the combination of the chip selection signal CS and thecommand-address signals CA at the rising edges T1˜T15 of the main clocksignal MCK.

Referring to FIG. 7, a first active command ACT1 and a first CAS commandRD1 for a first access operation may be transferred sequentially andthen a second active command ACT2 and a second CAS command RD2 for asecond access operation may be transferred sequentially. FIG. 7illustrates the read command RD as an example of the CAS command and theCAS command may be the write command WR.

In the first mode, the memory controller 200 in FIG. 2 may transmit thefirst active command ACT1 during the 4 clock cycles corresponding to the4 rising edges T1, T2, T3, and T4 of the main clock signal MCK, transmitthe first CAS command RD1 during the 2 clock cycles corresponding to the2 rising edges T5 and T6 after transmitting the first active commandACT1, transmit the second active command ACT2 during the 4 clock cyclescorresponding to the 4 rising edges T7, T8, T9, and T10 aftertransmitting the first CAS command RD1, and then transmit the second CAScommand RD2 during the 2 clock cycles corresponding to the 2 risingedges T11 and T12 after transmitting the second active command ACT2. Inthis case, the flag information SPL in the first active command ACT1 andthe second active command ACT2 may be at a first logic level (e.g.,logic low level L) to indicate the first mode. As a result, the tCCDbetween the two consecutive CAS commands RD1 and RD2 may correspond tothe 6 clock cycles 6tCK.

The control logic 410 in the memory device 400 of FIG. 3 may generate arow latch control signal LTR and a column latch control signal LTC andprovide them to the address register 420. The address register 420 maylatch the row addresses in the active commands ACT1 and ACT2 in responseto the row latch control signal LTR. The address register 420 may latchthe column addresses in the CAS commands RD1 and RD2 in response to thecolumn latch control signal LTC. For example, as illustrated in FIG. 7,the control logic 410 may activate the row latch control signal LTR in aform of 4 pulses when the active command ACT corresponding to the 4clock cycles is received. The control logic 410 may activate the columnlatch control signal LTC in a form of 2 pulses when the CAS command RDcorresponding to the 2 clock cycles is received.

The control logic 410 may control the activation timing of the row latchcontrol signal LTR based on the flag information SPL representingwhether the CAS command is inserted between the clock cycles of theactive command ACT. The control logic 410 may activate the row latchcontrol signal LTR in synchronization with the 4 consecutive risingedges T1, T2, T3, and T4 when the flag information in the first activecommand ACT1 is the logic low level L to indicate the first mode. Also,the control logic 410 may activate the row latch control signal LTR insynchronization with the 4 consecutive rising edges T7, T8, T9, and T10when the flag information in the second active command ACT2 is a logiclow level L to indicate the first mode.

FIG. 8 illustrates an example of data transfer in the first modeperformed in synchronization with the data clock signal WCK with theburst length of 16. In this case, the data transfer time tTR for oneaccess operation corresponds to the 4 clock cycles 4tCK of the mainclock signal MCK.

Referring to FIG. 8, transfer of the data bits 0˜15 may begin throughthe data bus or the data pin DQ after a predetermined latency LAT fromthe respective time points T6 and T12 when the CAS commands RD1 and RD2are received by the memory device through the control bus. The latencyLAT may be the read latency when the CAS command is the read command RDand the latency LAT may be the write latency when the CAS command is thewrite command WR. FIG. 8 illustrates the latency LAT of the one clockcycle for convenience of illustration. The latency LAT may be determinedvariously depending on the configuration of the memory system and/ortype of the access operation.

As illustrated in FIG. 8, the data transfer time tTR for the one accessoperation may be the four clock cycles 4tCK of the main clock signal MCKand the tCCD between the two consecutive CAS commands RD1 and RD2 may bethe 6 clock cycles 6tCK of the main clock signal MCK. As such, a DQbubble may be caused if the tCCD is longer than the data transfer timetTR. In this case, data transfer for the consecutive access operationsmay not be performed continuously due to the DQ bubble. The DQ bubblemay degrade utilization of the data bus by increasing the enable time ofthe data clock signal.

FIGS. 9 and 10 are timing diagrams illustrating an example of a signaltransfer and a command latch timing in a second mode. In particular,FIG. 9 illustrates command transfer and command latch timing in thesecond mode or the mixed mode when a first access operation and a secondaccess operation are performed successively. FIG. 10 illustratescorresponding data transfer. As described above, the command may bedetermined as the combination of the chip selection signal CS and thecommand-address signals CA at the rising edges T1˜T15 of the main clocksignal MCK.

Referring to FIG. 9, a first active command ACT1 and a first CAS commandRD1 for a first access operation may be transferred and a second activecommand ACT2 and a second CAS command RD2 for a second access operationmay be transferred. FIG. 9 illustrates the read command RD as an exampleof the CAS command and the CAS command may be the write command WR.

The memory controller 200 in FIG. 2 may transmit the first activecommand ACT1 during the 4 clock cycles corresponding to the 4 risingedges T1, T2, T3, and T4 of the main clock signal MCK in the first mode.After transmitting the first active command ACT1, the memory controller200 may transmit the second active command ACT2 and the first CAScommand RD1 in the second mode.

For example, the memory controller 200 may transmit the first portionACT2 a of the second active command ACT2 during the 2 clock cyclescorresponding to the 2 rising edges T5 and T6, transmit the first CAScommand RD1 during the 2 clock cycles corresponding to the 2 risingedges T7 and T8 after transmitting the first portion ACT2 a, andtransmit the second portion ACT2 b of the second active command ACT2during the 2 clock cycles corresponding to the 2 rising edges T9 andT10. After transmitting the second portion ACT2 b of the second activecommand ACT2, the memory controller 200 may transmit the second CAScommand RD2 during the 2 clock cycles corresponding to the 2 risingedges T11 and T12.

In this case, the flag information SPL in the first active command ACT1may be a first logic level (e.g., logic low level L) to indicate thefirst mode and the flag information in the second active command ACT2may be a second logic level (e.g., logic high level H) to indicate thesecond mode. As a result, the tCCD between the two consecutive CAScommands RD1 and RD2 may correspond to the 4 clock cycles 4tCK.

The control logic 410 in the memory device 400 of FIG. 3 may generate arow latch control signal LTR and a column latch control signal LTC andprovide them to the address register 420. The address register 420 maylatch the row addresses in the active commands ACT1 and ACT2 in responseto the row latch control signal LTR. The address register 420 may latchthe column addresses in the CAS commands RD1 and RD2 in response to thecolumn latch control signal LTC.

For example, as illustrated in FIG. 9, the control logic 410 mayactivate the row latch control signal LTR in a form of 4 pulses when theactive command ACT corresponding to the 4 clock cycles is received. Thecontrol logic 410 may activate the column latch control signal LTC in aform of 2 pulses when the CAS command RD corresponding to the 2 clockcycles is received. The control logic 410 may control the activationtiming of the row latch control signal LTR based on the flag informationSPL representing whether the CAS command is inserted between the clockcycles of the active command ACT. The control logic 410 may activate therow latch control signal LTR in synchronization with the 4 consecutiverising edges T1, T2, T3, and T4 when the flag information in the firstactive command ACT1 is a logic low level to indicate the first mode. Incontrast, the control logic 410 may activate the row latch controlsignal LTR in synchronization with the 4 non-consecutive rising edgesT5, T6, T9, and T10 when the flag information in the second activecommand ACT2 is a logic high level H to indicate the second mode.

The address register 420 in the memory device 400 may latch the secondportion ACT2 b of the second active command ACT2 after a standby timetWT from a time point T6 of latching the first portion ACT2 a of thesecond active command ACT2 in response to the row latch control signalLTR, when the flag information SPL represents that the other command(e.g., the first CAS command RD1) is inserted between the clock cyclesof the second active command ACT2. The standby time tWT may bedetermined based on mode register information provided from the memorycontroller 200 and stored in the mode register 412 in the memory device400 of FIG. 3. The mode register information may be provided through themode register write command MRW. The mode register write command MRW mayinclude the information OP0˜OP7 as illustrated in FIG. 4 to be writtenin the mode register 412.

FIG. 10 illustrates an example of data transfer in the second modeperformed in synchronization with the data clock signal WCK with theburst length of 16. In this case, the data transfer time tTR for oneaccess operation corresponds to the 4 clock cycles 4tCK of the mainclock signal MCK.

Referring to FIG. 10, transfer of the data bits 0˜15 may begin throughthe data bus or the data pin DQ after a predetermined latency LAT fromthe respective time points T8 and T12 when the CAS commands RD1 and RD2are received by the memory device through the control bus. The latencyLAT may be the read latency when the CAS command is the read command RDand the latency LAT may be the write latency when the CAS command is thewrite command WR. FIG. 10 illustrates the latency LAT of the one clockcycle for convenience of illustration and the latency LAT may bedetermined in various ways depending on configuration of the memorysystem and/or type of the access operation.

As illustrated in FIG. 10, the data transfer time tTR for the one accessoperation may be the four clock cycles 4tCK of the main clock signalMCK. The tCCD between the two consecutive CAS commands RD1 and RD2 maybe the 4 clock cycles 4tCK of the main clock signal MCK. As such, a DQbubble, for example, as illustrated in FIG. 8, may be removed if thetCCD is equal to the data transfer time tTR, and the data transfer forthe consecutive access operations may be performed continuously.

The memory system and the method of operating the memory systemaccording to example embodiments may therefore reduce the tCCD byadopting the second mode for mixing the two commands. Through thereduction of the tCCD, the DQ bubble, in which data transfer is notperformed continuously, may be prevented and utilization of the data busmay be enhanced.

FIG. 11 illustrating another example of commands that may be used in amemory system. In particular, FIG. 11 illustrates combinations of thechip selection signal CS and the command-address signals CA0˜CA8representing an active command ACT, a read command RD and a writecommand WR in the first mode or the normal mode and an active-readcommand ACT-RD and an active-write command ACT-WR in the second mode orthe mixed mode. Also, H indicates a logic high level, L indicates alogic low level, R0˜R16 indicate bits of a row address RA, BA0˜BA3indicate bits of a bank address BA, V indicates any one of the logic lowlevel and the logic high level, AP indicates auto-precharge, BLindicates a burst length, C4˜C9 indicate bits of a column address CA,and RE1˜RE4 indicate first through fourth rising edges of clock signalCK.

The memory controller 200 in FIG. 2 may combine two commands as a singlecombined command to transmit the single combined command in the secondmode. For example, as illustrated in FIG. 11, the read command RD andthe active command ACT in the normal mode may be combined as theactive-read command ACT-RD in the mixed mode. The write command WR andthe active command ACT in the normal mode may be combined as theactive-write command ACT-WR in the mixed mode. Each of the active-readcommand ACT-RD and the active-write command ACT-WR may include both therow address R0˜R16 and the column address C4˜C9.

FIG. 12 is a timing diagram illustrating example operations in a firstmode and a second mode. Referring to FIG. 12, the command may bedetermined as the combination of the chip selection signal CS and thecommand-address signals CA at the rising edges T1˜T9 of the main clocksignal MCK. The examples of the combination of the chip selection signalCS and the command-address signals CA are illustrated in FIG. 11. FIG.12 illustrates the command-address signals May in the first mode or thenormal mode and the command-address signals CAm in the second mode orthe mixed mode.

The first command may be transferred continuously during a plurality ofclock cycles in the first mode. The mixture of the first command and thesecond command may be transferred in the second mode. As illustrated inFIG. 12, the first command may be the active command ACT and the secondcommand may be the CAS command. FIG. 12 illustrates the read command RDas an example of the CAS command and the CAS command may be the writecommand WR.

The memory controller 200 in FIG. 2 may transmit the active command ACTduring the four clock cycles corresponding to the four rising edges T3,T4, T5, and T6 of the main clock signal MCK. The memory controller 200may then transmit the CAS command RD during the two clock cyclescorresponding to the two rising edges T7 and T8 in the first mode.

In one embodiment, the memory controller 200 may transmit the combinedactive-CAS command ACT-RD during the four clock cycles corresponding tothe four rising edges T1, T2, T3, and T4, and may transmit the nextcombined active-CAS command ACT-RD during the four clock cyclescorresponding to the four rising edges T5, T6, T7 and T8.

As illustrated in FIG. 12, the CAS-to-CAS delay time (tCCD)corresponding to the time duration between the two successive CAScommands may be reduced by adopting the second mode for mixing the twocommands. The tCCDn in the first mode corresponds to the 6 clock cyclesbut the tCCDm in the second mode may be reduced to the 4 clock cycles.Through the reduction of the tCCD, a DQ bubble, in which data transferis not performed continuously, may be prevented and utilization of thedata bus may be enhanced.

FIG. 13 is a timing diagram illustrating an example of a signal transferin a second mode. In particular, FIG. 13 illustrates command transferand command latch timing in the second mode when a first accessoperation and a second access operation are performed successively. Asdescribed above, the command may be determined as the combination of thechip selection signal CS and the command-address signals CA at therising edges T1˜T13 of the main clock signal MCK.

Referring to FIG. 13, a first active-CAS command ACT-RD1 for a firstaccess operation, a second active-CAS command ACT-RD2 for a secondaccess operation, and a third active-CAS command ACT-RD3 for a thirdaccess operation may be transferred successively from the memorycontroller to the memory device. FIG. 13 illustrates the active-readcommand ACT-RD as an example of the combined command and the combinedcommand may be the active-write command ACT-WR.

The memory controller 200 in FIG. 2 may transmit the first active-CAScommand ACT-RD1 during the 4 clock cycles corresponding to the 4 risingedges T1, T2, T3, and T4 of the main clock signal MCK in the secondmode, and may transmit the second active-CAS command ACT-RD2 during the4 clock cycles corresponding to the 4 rising edges T5, T6, T7, and T8 ofthe main clock signal MCK in the second mode. The memory controller 200may then transmit the third active-CAS command ACT-RD3 during the 4clock cycles corresponding to the 4 rising edges T9, T10, T11, and T12of the main clock signal MCK in the second mode. As a result, the tCCDbetween the two consecutive active-CAS commands ACT-RD1 and ACT-RD2 maycorrespond to the 4 clock cycles 4tCK.

FIG. 13 illustrates data transfer in the second mode which is performedin synchronization with the data clock signal WCK with the burst lengthof 16. In this case, the data transfer time tTR for one access operationcorresponds to the 4 clock cycles 4tCK of the main clock signal MCK.

Transfer of the data bits 0˜15 may begin through the data bus or thedata pin DQ after a predetermined latency LAT from the respective timepoints T4, T8, and T12 when the active-CAS commands ACT-RD1, ACT-RD2,and ACT-RD3 are received by the memory device through the control bus.The latency LAT may be the read latency when the combined command is theactive-read command ACT-RD. The latency LAT may be the write latencywhen the combined command is the active-write command ACT-WR. FIG. 13illustrates the latency LAT of the one clock cycle for convenience ofillustration. The latency LAT may be determined in various waysdepending on configuration of the memory system and/or type of theaccess operation.

As illustrated in FIG. 13, the data transfer time tTR for each accessoperation may be the four clock cycles 4tCK of the main clock signal MCKand also the tCCD between the two consecutive active-CAS commandsACT-RD1 and ACT-RD2 may be the 4 clock cycles 4tCK of the main clocksignal MCK. As such, a DQ bubble, for example, as illustrated in FIG. 8,may be removed if the tCCD is equal to the data transfer time tTR andthe data transfer for the consecutive access operations may be performedcontinuously.

The memory system and the method of operating the memory systemaccording to example embodiments may therefore reduce the tCCD byadopting the second mode for mixing the two commands. Through thereduction of the tCCD, the DQ bubble, in which data transfer is notperformed continuously, may be prevented and utilization of the data busmay be enhanced.

FIG. 14 illustrates an embodiment of a memory module 800 which includesa module substrate 810, a plurality of semiconductor memory chips SMCand a buffer chip BC. The semiconductor memory chips SMC may be mountedon the module substrate 810. Each of the semiconductor memory chips SMCmay receive data DQ from an external device such as a memory controllerthrough a data bus 812 in a write mode, or may transmit the data DQ tothe external device through the data bus 812 in a read mode.

The buffer chip BC may be mounted on the module substrate 810 and thebuffer chip BC may receive command signals CMD and address signals ADDthrough a control bus 511, to provide the received signals CMD and ADDto the semiconductor memory chips SMC through internal buses 513 and514. The buffer chip BC may include a register to store controlinformation of the memory module 800.

An external device, such as the memory controller, may selectivelyoperate in a first mode or a second mode. In the first mode, theexternal device may transmit a first command continuously during aplurality of clock cycles. In the second mode, the external device maymix a second command with the first command and may transmit the mixtureof the first command and the second command. Each of the semiconductormemory chips SMC may change command latch timing depending on the firstmode or the second mode. The tCCD may be reduced by adopting the secondmode for mixing the two commands. Through the reduction of the tCCD, aDQ bubble, in which data transfer is not performed continuously, may beprevented and utilization of the data bus may be enhanced.

FIG. 15 illustrates an embodiment of a stacked memory device 900 whichincludes first through kth semiconductor integrated circuit layers LA1through LAk. The lowest first semiconductor integrated circuit layer LA1may be a master layer. The other semiconductor integrated circuit layersLA2 through LAk may be slave layers.

The first through kth semiconductor integrated circuit layers LA1through LAk may transmit and receive signals between the layers bythrough-substrate vias (e.g., through-silicon vias (TSVs)). The lowestfirst semiconductor integrated circuit layer LA1, as the master layer,may communicate with an external memory controller through a conductivestructure formed on an external surface.

The first semiconductor integrated circuit layer 910 through the kthsemiconductor integrated circuit layer 920 may include memory regions921 and various peripheral circuits 922 for driving the memory regions921. For example, the peripheral circuits may include a row (X)-driverfor driving word lines of a memory, a column (Y)-driver for driving bitlines of the memory, a data input/output unit for controllinginput/output of data, a command buffer for receiving a command from anexternal device and buffering the command, and an address buffer forreceiving an address from an external device and buffering the address.

The first semiconductor integrated circuit layer 910 may further includecontrol logic which generates control signals to control the memoryregion 921 based on the command-address signals from the memorycontroller.

According to example embodiments, the semiconductor memory device 900may change command latch timing depending on the first mode or thesecond mode as described above. The tCCD may be reduced by adopting thesecond mode for mixing the two commands. Through the reduction of thetCCD, a DQ bubble, in which data transfer is not performed continuously,may be prevented and utilization of the data bus may be enhanced.

FIG. 16 illustrates an embodiment of a memory system 1000 which includesa memory module 1010 and a memory controller 1020. The memory module1010 may include at least one semiconductor memory device 1030 mountedon a module substrate. For example, the semiconductor memory device 1030may be constructed as a DRAM chip. In addition, the semiconductor memorydevice 1030 may include a stack of semiconductor dies. In some exampleembodiments, the semiconductor dies may include the master die 1031 andthe slave dies 1032. Signal transfer between the semiconductor chips mayoccur via through-substrate vias (e.g., TSVs) and/or bonding wires.

The memory module 1010 may communicate with the memory controller 1020via a system bus. Data DQ, a command/address CMD/ADD, and a clock signalCLK may be transmitted and received between the memory module 1010 andthe memory controller 1020 via the system bus.

As described above, the memory controller 1020 may selectively operatein a first mode, to transmit a first command continuously during aplurality of clock cycles, or in a second mode to mix a second commandwith the first command and transmit the mixture of the first command andthe second command. Each of the semiconductor memory chips 1030 maychange command latch timing depending on the first mode or the secondmode. The tCCD may be reduced by adopting the second mode for mixing thetwo commands. Through the reduction of the tCCD, a DQ bubble, in whichdata transfer is not performed continuously, may be prevented andutilization of the data bus may be enhanced.

FIG. 17 illustrates an embodiment of a mobile system 1200 which includesan application processor 1210, a connectivity unit 1220, a volatilememory device (VM) 1230, a nonvolatile memory device 1240, a userinterface 1250, and a power supply 1260. In some embodiments, the mobilesystem 1200 may be a mobile phone, a smart phone, a personal digitalassistant (PDA), a portable multimedia player (PMP), a digital camera, amusic player, a portable game console, a navigation system, or anothertype of electronic device.

The application processor 1210 may execute applications such as a webbrowser, a game application, a video player, etc. In some embodiments,the application processor 1210 may include a single core or multiplecores. For example, the application processor 1210 may be a multi-coreprocessor such as a dual-core processor, a quad-core processor, ahexa-core processor, etc. The application processor 1210 may include aninternal or external cache memory.

The connectivity unit 1220 may perform wired or wireless communicationwith an external device. For example, the connectivity unit 1220 mayperform Ethernet communication, near field communication (NFC), radiofrequency identification (RFID) communication, mobile telecommunication,memory card communication, universal serial bus (USB) communication,etc. In some embodiments, connectivity unit 1220 may include a basebandchipset that supports communications, such as global system for mobilecommunications (GSM), general packet radio service (GPRS), wideband codedivision multiple access (WCDMA), high speed downlink/uplink packetaccess (HSxPA), etc.

The volatile memory device 1230 may store data processed by theapplication processor 1210, or may operate as a working memory. Forexample, the volatile memory device 1230 may be a dynamic random accessmemory, such as DDR SDRAM, LPDDR SDRAM, GDDR SDRAM, RDRAM, etc. Thenonvolatile memory device 1240 may store a boot image for booting themobile system 1200. For example, the nonvolatile memory device 1240 maybe an electrically erasable programmable read-only memory (EEPROM), aflash memory, a phase change random access memory (PRAM), a resistancerandom access memory (RRAM), a nano floating gate memory (NFGM), apolymer random access memory (PoRAM), a magnetic random access memory(MRAM), a ferroelectric random access memory (FRAM), etc.

The application processor 1210 may generate commands for controlling thememory devices 1230 and 1240. The application processor 1210 mayselectively operate in a first mode to transmit a first commandcontinuously during a plurality of clock cycles or in a second mode tomix a second command with the first command and transmit a mixture ofthe first command and the second command. Each of the memory devices1230 and 1240 may change command latch timing depending on the firstmode or the second mode. The tCCD may be reduced by adopting the secondmode for mixing the two commands. Through the reduction of the tCCD, theDQ bubble, in which data transfer is not performed continuously, may beprevented and utilization of the data bus may be enhanced.

The user interface 1250 may include at least one input device, such as akeypad, a touch screen, etc., and at least one output device, such as aspeaker, a display device, etc. The power supply 1260 may supply a powersupply voltage to the mobile system 1200. In some embodiments, themobile system 1200 may further include a camera image processor (CIS),and/or a storage device, such as a memory card, a solid state drive(SSD), a hard disk drive (HDD), a CD-ROM, etc.

In some embodiments, the mobile system 1200 and/or components of themobile system 1200 may be packaged in various forms. Examples includepackage-on-package (PoP), ball grid arrays (BGAs), chip scale packages(CSPs), plastic leaded chip carrier (PLCC), plastic dual in-line package(PDIP), die-in-waffle pack, die-in-wafer form, chip-on-board (COB),ceramic dual in-line package (CERDIP), plastic metric quad flat pack(MQFP), thin quad flat pack (TQFP), small outline IC (SOIC), shrinksmall outline package (SSOP), thin small outline package (TSOP),system-in-package (SIP), multi-chip package (MCP), wafer-levelfabricated package (WFP), wafer-level processed stack package (WSP),etc.

FIG. 18 illustrates an embodiment of a computing system 1300 whichincludes a processor 1310, an input/output hub (IOH) 1320, aninput/output controller hub (ICH) 1330, at least one memory module 1340,and a graphics card 1350. In some embodiments, the computing system 1300may be a personal computer (PC), a server computer, a workstation, alaptop computer, a mobile phone, a smart phone, a personal digitalassistant (PDA), a portable multimedia player (PMP), a digital camera),a digital television, a set-top box, a music player, a portable gameconsole, navigation system, etc.

The processor 1310 may perform various computing functions such asexecuting specific software for performing specific calculations ortasks. For example, the processor 1310 may be a microprocessor, acentral process unit (CPU), a digital signal processor, or the like. Insome embodiments, the processor 1310 may include a single core ormultiple cores. For example, the processor 1310 may be a multi-coreprocessor, such as a dual-core processor, a quad-core processor, ahexa-core processor, etc. Although FIG. 18 illustrates the computingsystem 1300 including one processor 1310, in some embodiments, thecomputing system 1300 may include a plurality of processors. Theprocessor 1310 may include an internal or external cache memory.

The processor 1310 may include a memory controller 1311 for controllingoperations of the memory module 1340. The memory controller 1311included in the processor 1310 may be referred to as an integratedmemory controller (IMC). A memory interface between the memorycontroller 1311 and the memory module 1340 may be implemented with asingle channel including a plurality of signal lines, or may bay beimplemented with multiple channels, to each of which at least one memorymodule 1340 may be coupled. In some embodiments, the memory controller1311 may be located inside the input/output hub 1320, e.g., a memorycontroller hub (MCH).

The memory module 1340 may include at least one memory chip. The memorycontroller 1311 may selectively operate in a first mode to transmit afirst command continuously during a plurality of clock cycles or in asecond mode to mix a second command with the first command and transmita mixture of the first command and the second command. The chip in thememory module 1340 may change command latch timing depending on thefirst mode or the second mode. The tCCD may be reduced by adopting thesecond mode for mixing the two commands. Through the reduction of thetCCD, a DQ bubble, in which data transfer is not performed continuously,may be prevented and utilization of the data bus may be enhanced.

The input/output hub 1320 may manage data transfer between processor1310 and devices, such as the graphics card 1350. The input/output hub1320 may be coupled to the processor 1310 via various interfaces. Forexample, the interface between the processor 1310 and the input/outputhub 1320 may be a front side bus (FSB), a system bus, a HyperTransport,a lightning data transport (LDT), a QuickPath interconnect (QPI), acommon system interface (CSI), etc.

Although FIG. 18 illustrates the computing system 1300 including oneinput/output hub 1320, in some embodiments, the computing system 1300may include a plurality of input/output hubs. The input/output hub 1320may provide various interfaces with the devices. For example, theinput/output hub 1320 may provide an accelerated graphics port (AGP)interface, a peripheral component interface-express (PCIe), acommunications streaming architecture (CSA) interface, etc.

The graphic card 1350 may be coupled to the input/output hub 1320 viaAGP or PCIe. The graphics card 1350 may control a display device (notshown) for displaying an image. The graphics card 1350 may include aninternal processor for processing image data and an internal memorydevice. In some embodiments, the input/output hub 1320 may include aninternal graphics device along with or instead of the graphics card 1350outside the graphics card 1350. The graphics device included in theinput/output hub 1320 may be referred to as integrated graphics.Further, the input/output hub 1320 including the internal memorycontroller and the internal graphics device may be referred to as agraphics and memory controller hub (GMCH).

The input/output controller hub 1330 may perform data buffering andinterface arbitration to efficiently operate various system interfaces.The input/output controller hub 1330 may be coupled to the input/outputhub 1320 via an internal bus, such as a direct media interface (DMI), ahub interface, an enterprise Southbridge interface (ESI), PCIe, etc. Theinput/output controller hub 1330 may provide various interfaces withperipheral devices. For example, the input/output controller hub 1330may provide a universal serial bus (USB) port, a serial advancedtechnology attachment (SATA) port, a general purpose input/output(GPIO), a low pin count (LPC) bus, a serial peripheral interface (SPI),PCI, PCIe, etc.

In some embodiments, the processor 1310, the input/output hub 1320 andthe input/output controller hub 1330 may be implemented as separatechipsets or separate integrated units. In other embodiments, at leasttwo of the processor 1310, the input/output hub 1320 and theinput/output controller hub 1330 may be implemented as a single chipset.Also, while many features of the embodiments are disclosed as units, inother embodiments those features may be implemented as other forms oflogic including but not limited to code-based operations performed by aprocessor.

The memory system and the method of operating the memory systemaccording to example embodiments may reduce a CAS-to-CAS delay time(tCCD) or maintain the tCCD in a minimum value by adopting an operationfor mixing two commands. Through the reduction of the tCCD, a DQ bubble,in which data transfer is not performed continuously, may be preventedand utilization of a data bus may be enhanced.

The embodiments described herein may be applied to arbitrary devices andsystems including a memory device. For example, the embodiments may beapplied to a mobile phone, a smart phone, a personal digital assistant(PDA), a portable multimedia player (PMP), a digital camera, acamcorder, personal computer (PC), a server computer, a workstation, alaptop computer, a digital TV, a set-top box, a portable game console, anavigation system, etc.

In accordance with another embodiment, an apparatus includes aninterface coupled to a memory. The interface may be one or more ofsignal or bus lines corresponding to the aforementioned embodiments. Thememory controller selectively operates in a first mode and a secondmode. The memory controller transmits a first command continuouslythrough the interface during a plurality of clock cycles in the firstmode. The memory controller mixes a second command with the firstcommand and transmits the mixture of the first command and the secondcommand through the interface in the second mode. The memory controllermay insert the second command between the clock cycles of the firstcommand in the second mode. The memory controller may include flaginformation in the first command transmitted through the interface tothe memory, wherein the flag information is indicative of a change incommand latch timing for the memory. The memory controller maycorrespond to the memory controller in any of the aforementionedembodiments.

The methods, processes, and/or operations described herein may beperformed by code or instructions to be executed by a computer,processor, controller, or other signal processing device. The computer,processor, controller, or other signal processing device may be thosedescribed herein or one in addition to the elements described herein.Because the algorithms that form the basis of the methods (or operationsof the computer, processor, controller, or other signal processingdevice) are described in detail, the code or instructions forimplementing the operations of the method embodiments may transform thecomputer, processor, controller, or other signal processing device intoa special-purpose processor for performing the methods herein.

The controllers, control logic, decoders, and other processing featuresof the embodiments described herein may be implemented in logic which,for example, may include hardware, software, or both. When implementedat least partially in hardware, the controllers, control logic,decoders, and processing features may be, for example, any one of avariety of integrated circuits including but not limited to anapplication-specific integrated circuit, a field-programmable gatearray, a combination of logic gates, a system-on-chip, a microprocessor,or another type of processing or control circuit.

When implemented in at least partially in software, the controllers,control logic, decoders, and other processing features may include, forexample, a memory or other storage device for storing code orinstructions to be executed, for example, by a computer, processor,microprocessor, controller, or other signal processing device. Thecomputer, processor, microprocessor, controller, or other signalprocessing device may be those described herein or one in addition tothe elements described herein. Because the algorithms that form thebasis of the methods (or operations of the computer, processor,microprocessor, controller, or other signal processing device) aredescribed in detail, the code or instructions for implementing theoperations of the method embodiments may transform the computer,processor, controller, or other signal processing device into aspecial-purpose processor for performing the methods herein.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation. In someinstances, as would be apparent to one of skill in the art as of thefiling of the present application, features, characteristics, and/orelements described in connection with a particular embodiment may beused singly or in combination with features, characteristics, and/orelements described in connection with other embodiments unless otherwiseindicated. Accordingly, it will be understood by those of skill in theart that various changes in form and details may be made withoutdeparting from the spirit and scope of the embodiments set forth in theclaims.

What is claimed is:
 1. A memory system, comprising: a memory controllerto selectively operate in a first mode and a second mode, the memorycontroller to transmit a first command continuously during a pluralityof clock cycles in the first mode and the memory controller to mix asecond command with the first command and transmit the mixture of thefirst command and the second command in the second mode; and a memory tochange command latch timing depending on the first mode or the secondmode.
 2. The memory system as claimed in claim 1, wherein the memorycontroller is to insert the second command between the clock cycles ofthe first command in the second mode.
 3. The memory system as claimed inclaim 2, wherein the memory is to receive flag information representingwhether the second command is inserted between the clock cycles of thefirst command.
 4. The memory system as claimed in claim 3, wherein: whenthe flag information represents that the second command is insertedbetween the clock cycles of the first command, the memory is to latch asecond portion of the first command after a standby time from a timepoint of latching a first portion of the first command.
 5. The memorysystem as claimed in claim 4, wherein the standby time is to bedetermined based on mode register information provided from the memorycontroller and is to be stored in a mode register of the memory.
 6. Thememory system as claimed in claim 3, wherein the memory controller is togenerate the first command including the flag information.
 7. The memorysystem as claimed in claim 1, wherein the memory controller is tocombine the first command and the second command as a third command totransmit the third command in the second mode.
 8. The memory system asclaimed in claim 7, wherein the third command includes a row address anda column address.
 9. The memory system as claimed in claim 1, wherein:the first command is an active command including a row address, and thesecond command is a column address strobe (CAS) command including acolumn address.
 10. The memory system as claimed in claim 9, wherein thememory controller is to: transmit the active command during 4 clockcycles and transmit the CAS command during 2 clock cycles aftertransmitting the active command in the first mode; and transmit a firstportion of the active command during 2 clock cycles, transmit the CAScommand during 2 clock cycles after transmitting the first portion ofthe active command, and transmit a second portion of the active commandafter transmitting the CAS command in the second mode.
 11. The memorysystem as claimed in claim 9, wherein the memory controller is to:transmit the active command during 4 clock cycles and transmit the CAScommand during 2 clock cycles after transmitting the active command inthe first mode; and combine the first command and the second command asa third command and transmit the third command during 4 clock cycles inthe second mode.
 12. The memory system as claimed in claim 9, wherein adata transfer time for a single access operation is substantially equalto a CAS-to-CAS delay time (tCCD) between two sequential CAS commandsfor two sequential access operations.
 13. The memory system as claimedin claim 9, wherein, when a first access operation and a second accessoperation are performed successively, the memory controller is to:transmit a first active command for the first access operation; transmita first portion of a second active command for the second accessoperation after transmitting the first active command; transmit a firstCAS command for the first access operation after transmitting the firstportion of the second active command; transmit a second portion of thesecond active command after transmitting the first CAS command; andtransmit a second CAS command for the second access operation aftertransmitting the second portion of the second active command.
 14. Thememory system as claimed in claim 1, wherein the memory is athree-dimensional semiconductor memory including a plurality ofsemiconductor dies that are stacked vertically.
 15. A memory system,comprising: a memory controller to selectively operate in a first modeand a second mode, the memory controller to transmit an active commandincluding a row address continuously during a plurality of clock cyclesin the first mode and the memory controller to mix a column addressstrobe (CAS) command including a column address with the active commandand transmit a mixture of the active command and the CAS command in thesecond mode; and a memory device to change command latch timingdepending on the first mode or the second mode.
 16. An apparatus,comprising: an interface coupled to a memory; and a memory controller toselectively operate in a first mode and a second mode, the memorycontroller to transmit a first command continuously through theinterface during a plurality of clock cycles in the first mode and tomix a second command with the first command and transmit the mixture ofthe first command and the second command through the interface in thesecond mode, wherein the memory controller is to insert the secondcommand between the clock cycles of the first command in the secondmode.
 17. The apparatus as claimed in claim 16, wherein the memorycontroller is to include flag information in the first commandtransmitted through the interface to the memory, wherein the flaginformation is indicative of a change in command latch timingcorresponding to the memory.